Vehicles conventionally use a mechanically driven coolant pump that is integrated with the engine to cool the engine and other sub-systems on the vehicle. These mechanically driven coolant pumps are typically tied to the engine speed by a gear ratio so that when the engine is running the coolant flow is greater at higher speeds than when the engine is at lower speeds. In addition, no coolant flow is provided when the engine is shut down.
For certain vehicles, components other than the engine are connected to the coolant system so that the coolant flow also provides cooling of these components. These components retain heat when the engine is shut down and thus are subject to various heat related conditions, such as heat soak, thermal meltdowns, and reduced durability.
There is also increased use of electrified systems on vehicles. One example is a typical hybrid electric vehicle (HEV) which includes an engine and a number of electric components like electric generators, electric motors, power electronics like DC/AC inverters, DC/DC converters, and energy storage technologies like super capacitors and/or batteries. Other vehicles may employ an on-board generating system that includes electric generators and power electronics like DC/AC inverters and/or DC/DC converters. There are several other examples of vehicles that employ electric accessories including the motors and power electronics to drive the accessories. Also, there are completely electrified vehicles like battery electric vehicles (BEV) or fuel cell vehicles (FCV) that do not have any engine cooling loop available to cool any of their components.
Such electrified systems and other components of the vehicle have substantially different cooling needs than the engine (if provided), and the mechanically driven coolant system often struggles to satisfy these needs. For example, electric components have different cooling requirements such as different temperature thresholds and coolant flow rates than the engine and even different requirements among one another, and may be required to operate when the engine is shut down. Mechanical components such as air compressors, exhaust gas recirculation valves, and turbochargers also have cooling requirements that differ from the cooling requirements of the engine, and also often have to operate when the engine is shut down, or retain heat after the engine is shut down. Therefore, further improvements are needed to enable non-engine components of vehicles to operate at higher efficiencies, improve performance, and/or improve the operating life and durability.